8 Replies Latest reply on Jun 19, 2008 3:45 AM by

    Basic resolution adjustment

    pbsue
      I am trying to save a .png as a .gif with a resolution high enough to print. It seems set at 72 by default. When I change it to something higher, it isn't maintained when I export as a .gif. Then when I change the .gif to a higher resolution that doesn't stay maintained. I don't know what I am doing wrong.

      Thanks, Sue
        • 1. Re: Basic resolution adjustment
          Level 7
          On Sat, 7 Jun 2008, pbsue wrote

          >I am trying to save a .png as a .gif with a resolution high enough to
          >print. It seems set at 72 by default. When I change it to something
          >higher, it isn't maintained when I export as a .gif. Then when I change
          >the .gif to a higher resolution that doesn't stay maintained. I don't
          >know what I am doing wrong.

          For an image created on a computer the so called dpi value is there for
          determining the size the image will be printed, and has nothing to do
          with the inherent quality of the image or "high resolution".

          Image width in pixels divided by stored dpi value = print width in
          inches
          Image height in pixels divided by stored dpi value = print height in
          inches

          The dpi value stored in an image file has no value as an indicator of
          quality except when scanning a document, which is a different case.
          http://www.emdpi.com/imagedpi.html

          There is a 'gotcha' with a gif file in that a gif does _not_ store a dpi
          value. When saving to a gif from any other format the dpi value is
          discarded. When reading a gif file the graphic software often 'invents'
          a dpi value it likes. Get the free Irfanview at
          http://www.irfanview.net/ , open a gif, and look at image ->
          information. You will see that the DPI fields [1] are blank because
          there is no dpi information stored in a gif file. Open it in some other
          graphics app and you will likely see an invented value like 72

          [1] There are two dpi fields because most graphic file formats have both
          a width dpi value and a height dpi value that, in most cases, have the
          same value.

          --
          Richard Mason
          http://www.emdpi.com
          • 2. Re: Basic resolution adjustment
            pbsue Level 1
            Richard,

            Thanks for the reply. Just as I suspected, I was missing some basic understanding.

            I visited the two sites you referenced and am trying to assimilate the info you provided.

            So, to create an image in fireworks that is of high enough resolution for printing I need to set the pixel size of the image or canvas and then set the print size (in the image size dialog box) and even though it will give a dpi, that is irrelevant.

            Example: if I set the print size to 2 inches and the pixel width and height to 500 the dpi will say 250 pixels/square inch but when I export it to a .gif it will still say 500 pixels wide for the image but it will say 72dpi. So, in this case what is the reality of the resolution of the image once the .gif is created?

            Is this the way to get a print resolution ready image in Fireworks?

            Thanks, Sue
            • 3. Re: Basic resolution adjustment
              pixlor Level 4
              Figure out what size in pixels you need the image to be to print well, then make your image in Fireworks that many pixels.

              You need to know what the recommended dpi is for your output device and plan accordingly. You say you need "high enough resolution to print." How high is high? Do you have a high resolution printer (say 4800 dpi) and you are printing a piece to be held in the hand? (Then use a high dpi to calculate with.) Are you printing a large banner to be seen from across the room? (Then you can use a lower dpi.) Are you printing on an inherently low-resolution medium, like fabric?

              For example, if I wanted to make a t-shirt at CafePress, and I wanted to make the maximum size image (10 inches square) and I also went with their minimum recommendations for dpi (200 dpi), then I would make my image 2000 pixels square.

              Note that a 2000-pixel image can be printed at 2.5 inches for an effective 800 dpi or at 20 inches for an effective 100 dpi. It isn't the dpi that determines the information content in the image, it's the pixels. An image can be stretched or shrunk to any physical dimension, what you want to do is have the image be the smallest it can be to look good at the dimension you plan to print it.



              • 4. Re: Basic resolution adjustment
                Level 7
                On Sun, 8 Jun 2008, pbsue wrote
                >
                > So, to create an image in fireworks that is of high enough resolution for
                >printing I need to set the pixel size of the image or canvas and then set the
                >print size (in the image size dialog box) and even though it will give a dpi,
                >that is irrelevant.

                Print size, pixels size, and dpi are intimately related and dpi isn't
                irrelevant.
                pixel size divided by print size in inches = dpi
                and
                pixel size divided by dpi = print size in inches

                Pixels/inch and dpi are the same thing in this context.

                dpi doesn't mean what a lot of books and tutorials tell you it means.
                It's irrelevant for automatically determining the quality of an image
                unless you know for a fact that the dpi is actually the sampling
                resolution (pixels/inch) obtained from a scanning process.
                When you use the term 'high resolution' in relation to an image I assume
                you mean an image that is high quality in terms of image detail, and you
                can't tell that from a dpi value unless you _know_ that it's an image
                sampling value.

                One often sees that because an image is set at 300dpi it has 'high
                resolution'. Here's a cunning ploy. Give someone an image set at 50 dpi
                say. When they complain it's "not a high resolution image" just use
                Irfanview to change the stored dpi to 300 and give them back exactly the
                same image. Now I bet they say "that's better, a high resolution image"
                even though it's exactly the same image.

                > Example: if I set the print size to 2 inches and the pixel width and
                >height to
                >500 the dpi will say 250 pixels/square inch but when I export it to a .gif it
                >will still say 500 pixels wide for the image but it will say 72dpi.

                250 pixels/inch not square inch.

                If you export to a gif then that's when the dpi value becomes irrelevant
                because that dpi value can't be stored in the gif file format. The
                reason it says 72 is because when the gif is opened in Fireworks the
                program has no idea what dpi you intended because there is no dpi value
                stored in the gif file. Fireworks invents the value of 72 dpi for you!
                It's still exactly the same image you exported! If I open any gif image
                in Paint Shop Pro it tells me the image is 99 dpi because that's what is
                set as a default when the image file doesn't contain a dpi value. I said
                try Irfanview. It doesn't tell lies.

                >So, in this
                >case what is the reality of the resolution of the image once the .gif is
                >created?

                It's whatever you want it to be. When we talk about a high resolution
                image we think of this as 'good' because a high resolution image means
                lots of detail. The dpi value associated with an image is there only to
                enable us to determine the _printed_ size of the image but because the
                dpi value is also called 'resolution' people automatically think it is a
                measure of the 'goodness' of an image. It isn't when the image is
                created on a computer!! It is when the image is obtained via a sampling
                process!!

                > Is this the way to get a print resolution ready image in Fireworks?
                If you're talking about a print shop then Fireworks is not the program
                to use and gif is the wrong format. Others can give better advice on
                what program to use.

                If you just mean it will be printed on a laser, or whatever, then you
                just juggle two of the values in the above equations to get the desired
                result.

                --
                Richard Mason
                http://www.emdpi.com
                • 5. Re: Basic resolution adjustment
                  pbsue Level 1
                  Thank You Richard and Lorraine,

                  I have a fundamental understanding of this now. I'll let you know how the printing turns out.

                  Sue
                  • 6. Re: Basic resolution adjustment
                    thegendreamer
                    Thanks id like to hear how it goes too
                    • 7. Re: Basic resolution adjustment
                      pbsue Level 1
                      Well, I used the info I learned about pixel dimensions and dpi and created a .jpg instead of a .gif which was then printed/photocopied onto business cards that turned out great.

                      Thanks to Richard and Lorraine!
                      • 8. Re: Basic resolution adjustment
                        website and the basic infirmation which i was unable to understand earlier have solved the issues. thanks fro that advice